Thanks @xisco and apologies @Gruk. That screenshot was a bit wacky. I don’t know why the create was above the delete. sorry. 
Here is the latest screenshot:
I’m trying to destroy zombies on the screen with a click if the cursor is over them and if the cursor is not over a zombie when clicked then a target is put down which the player starts walking towards.
The solution, I think, has something to do with the cursor not being over every instance of a zombie. Because the desired effect works when there is only one zombie left.
I’ve tried swapping the touch and cursor over inverted events. And I’ve tried putting them in the and logic and as suggested elsewhere in the forums in the Not logic:
I cannot work out how to make the cursor over object inverted event cover every instance of the objects.
Here’s the game to test:
http://gd-games.s3-website-eu-west-1.amazonaws.com/game-1558090356539/